1. Field of the Invention
The present invention relates to the manufacture of capacitors and pyroelectric sensors, and more particularly, the invention relates to a method for manufacturing capacitors and pyroelectric sensors by transferring thin film material layers using hydrogen ion splitting technology.
2. Background of the Invention
There is much interest in the art in cost-effective ways to improve the manufacture of electrical devices such as capacitors and pyroelectric sensors. These devices are often made by placing thin film functional materials over CMOS or GaAs semi-conductor circuitry, or another suitable substrate. The thin film materials are typically ferroelectric, piezoelectric, pyroelectric, thermoelectric, high dielectric constant, electro-optic, photoreactive, wave guide, non-linear optical, superconducting, photodetecting, wide bandgap, electrically conducting, or have other desired qualities.
The thin film materials can be used for such devices as capacitors, high dielectric constant decoupling capacitors for power supplies, tunable microwave capacitors, pyroelectric un-cooled infrared imagers, boulometer infrared sensors, uncooled infrared detectors, cryogenic infrared detectors, and photodetectors.
To obtain high quality thin film material, the material is typically grown on a substrate at a growth temperature or annealing temperature of 500xc2x0 C. to 1100xc2x0 C. The high growth temperature is required to assure a high quality thin film material.
However, the highest temperature that a substrate containing CMOS integrated circuit technology can withstand, especially when metal interconnectors between circuitry layers are in place, is typically 450xc2x0 C. to 500xc2x0 C. Therefore, it is generally not possible to obtain the best quality thin film material by growing the material directly on a CMOS substrate.
An optimal solution is to grow the thin film material on a first, or growth, substrate, such as silicon, that can withstand the increased temperatures and then transfer the thin film material after it is grown to a second, or application, substrate such as the CMOS circuitry herein for use. However, there have been problems with isolating, and then transferring, the thin film layer. If the growth substrate is chemically or plasma etched away, mechanically or thinned using lappling and grinding, the risk of damage to the thin film layer during this process is considerable. Further, some growth substrate materials are very expensive, and elimination of the substrate to isolate the thin film layer is cost prohibitive. Once the thin film layer is separated from the growth substrate, there is a second problem. The thin film layer must have a smooth surface for the transition and bonding to the second substrate to be successful. Otherwise, the bond may not hold properly, and the device will not function optimally.
There have been attempts in the prior art to address this issue. Prior art of interest includes U.S. Pat. No. 6,120,597 to Levy et al.; U.S. Pat. No. 6,103,597 to Aspar et al.; U.S. Pat. No. 6,020,252 to Aspar et al.; U.S. Pat. No. 5,994,207 to Henley et al.; U.S. Pat. No. 5,993,677 to Biasse et al.; U.S. Pat. No. 5,966,620 to Sakaguchi et al.; U.S. Pat. No. 5,877,070 to Goesele et al.; and U.S. Pat. No. 5,654,583 to Okuno et al.
The Levy et al, Aspar et al (""597), Aspar et al (""252), Henley et al. (""207), Biasse, Sakaguchi et al., and Goesele et al. patents each disclose methods which utilize, to some extent, ion implantation, wafer bonding, and layer splitting for the transfer of semiconductor films to second substrates. For example, the Levy et al patent discloses a method of crystal ion slicing of single-crystal films, which is particularly useful in connection with metal oxide films and crystal structures. The Biasse et al. patent discloses a method for transferring a thin film from an initial substrate to a final substrate by joining the thin film to a handle substrate, cleaving the initial substrate, joining the thin film to a final substrate, and cleaving the handle substrate. The Goesele et al. patent discloses a method of transferring thin monocrystalline layers to second substrates at lower temperatures than previously possible. The Okuno et al. patent discloses a method for direct bonding different semiconductor structures in order to form a unified semiconductor device. However, these prior art references fail to provide a satisfactory answer to the problems of isolating and transferring the thin film layer described herein.
In accordance with the invention, a method is provided for fabricating capacitors and pyroelectric sensors by transferring thin film layers with the use of a hydrogen ion splitting technique.
In one embodiment, the method comprises the steps of optionally depositing at least one protective layer on one surface of a large diameter growth substrate; growing a film layer of thin film functional material on the at least one protective layer, the functional material comprising a material selected from the group consisting of ferroelectric, piezoelectric, pyroelectric, thermoconductive, high dielectric, electro optic, photorefractive, wave guide, non-linear optical, superconducting, photodetecting, wide bandgap, and electrically conducting materials; implanting hydrogen to a selected depth within the growth substrate or within the at least one protective layer to form a hydrogen ion layer so as to divide the material having the growth substrate and the at least one protective layer into distinct portions; bonding the growth substrate including the at least one protective layer and the thin film layer to a second substrate; splitting the material having the growth substrate and the at least one protective layer along the implanted ion layer and removing the portion of the material which is on the side of the ion layer away from the second substrate.
Preferably, the second substrate comprises silicon; the at least one protective layer further comprises an oxide layer, an adhesion layer, and a barrier layer; and the method further comprises the steps of; depositing the oxide layer on the silicon substrate for isolating the silicon substrate; depositing the adhesion layer on the oxide layer, wherein the adhesion layer is comprised of titanium; and depositing the barrier layer on the titanium adhesion layer for isolating the thin film layer, wherein the barrier layer comprises a material selected from a group consisting of platinum and iridium.
Advantageously, the barrier layer further comprises platinum and has a thickness of about 100 nm; the titanium adhesion layer has a thickness of about 50 nm; and the oxide layer further comprises silicon oxide and has a thickness of about 100 nm. Alternatively, the at least one protective layer further comprises MgO.
Advantageously, the method further comprises the step of implanting boron at the same selected depth as the implanted hydrogen for lowering the thermal energy required to split the growth substrate.
Preferably, the method further comprises the step of depositing at least one layer of metal on the thin film layer before the bonding step.
Advantageously, the at least one layer of metal comprises a metal selected from a group consisting of gold, palladium, platinum and nickel. Alternatively, the at least one layer of metal further comprises a layer of chrome, and a layer selected from the group consisting of gold and silver.
Preferably, the bonding step is carried out by bump bonding, and further comprises the step of depositing a layer of stiffener material on the thin film layer for providing mechanical support to the thin film layer.
Advantageously, the stiffener material comprises gold having a thickness of about 20 um.
Preferably, a portion of the second substrate comprises a type of circuitry selected from one of a group consisting of GaAs circuitry and CMOS circuitry.
Advantageously, the method further comprises the steps of depositing a layer comprising silicon on the surface of the second substrate before the bonding step, and fabricating at least one conductive connection from the circuitry to the layer of silicon at the surface of the second substrate.
Preferably, the method further comprises the steps of depositing a layer comprising a metal on the surface of the second substrate, and fabricating at least one conductive connection from the circuitry to the metal layer on the surface of the second substrate.
Advantageously, the second substrate is comprised of a material selected from a group consisting of glass, quartz, poly-SiC, GaAs, silicon, diamond, and sapphire.
Preferably, the method further comprises the step of annealing the thin film layer for strengthening and tempering the thin film layer, and wherein the anneal is carried out at a temperature of about 600xc2x0 C. to about 1100xc2x0 C.
Advantageously, the thin film layer comprises a material selected from a group consisting of nanoparticles, PZT, SrBaTiO3, PLZT and LiNbO3.
Preferably, the thin film layer comprises a material selected from a group consisting of SiGe, GaAs, CdTe/HgCdTe, ZnO and GaN.
Advantageously, the large diameter growth substrate comprises a material selected from a group consisting of silicon, GaAs, sapphire and quartz.
Preferably, the large diameter growth substrate comprises silicon.
Preferably, the second substrate further comprises a material selected from a group consisting of silicon, glass, quartz, poly-SiC, GaAs, diamond, and sapphire.
In an alternative embodiment, the film layer of thin film functional material is grown directly on the surface of the growth substrate. The hydrogen ion layer is implanted within the growth substrate, and the growth substrate is split along the implanted ion layer.
Yet another embodiment is provided for making a pyroelectric sensor, comprising the steps of: depositing at least one protective layer on the surface of a growth substrate; growing a layer of pyroelectric thin film functional material on the at least one protective layer; implanting hydrogen to a selected depth within the growth substrate or within the at least one protective layer to form a hydrogen ion layer so as to divide the material having the growth substrate and the at least one protective layer into distinct portions; depositing at least one layer of metal on the pyroelectric thin film layer; providing a conductive connection between the material having the thin film layer, and a second substrate, the second substrate comprising circuitry; splitting the material having the growth substrate and the at least one protective layer along the implanted ion layer and removing the portion of the material which is on the side of the ion layer away from the second substrate.
Preferably, the method, further comprises the step of depositing a membrane layer on the at least one metal layer.
Advantageously, the membrane layer further comprises a nitride, and the method further comprises the step of removing a quantity of dielectric material from the nitride membrane.
Preferably, the method further comprises the step of providing a vacuum between the growth substrate and the second substrate.
Advantageously, providing the conductive connection is carried out by fabricating a conductive connection between the circuitry of the second substrate and the at least one metal layer. Alternatively, providing the conductive connection is carried out by fabricating a conductive connection between the second substrate circuitry and the second substrate surface; depositing a conductive layer on the surface of the second substrate, wherein the conductive layer is in contact with the conductive connection; and fabricating at least one post extending from the conductive layer to the metal layer for thermally insulating the CMOS or GaAs circuitry from the thin film pyroelectric layer, the at least one post comprising a material selected from one of a group consisting of a conductive epoxy, amorphous silicon, and InSnO.
In an alternative embodiment, the layer of pyroelectric thin film functional material is grown on the surface of the growth substrate; the hydrogen is implanted within the growth substrate, and the growth substrate is split along the implanted ion layer.
Other features and advantages of the invention will be set forth in, or will be apparent from, the detailed description of preferred embodiments of the invention, which follows.